Technical Field
The present invention relates to gas-insulated high-voltage circuit breakers and more particularly to circuit breakers having particle traps.
State of the Prior Art
In circuit breakers (eg. dead-tank circuit breaker, Gas Insulated Switchgear (GIS), etc.), the presence or generation of particles of dielectric or metallic material (for example, by parts which rub mechanically against one another or by the damage and surface wear of the arcing contacts caused by the formation of electric arcs) inside the tank (breaking chamber enclosure) can trigger a voltage breakdown between live and grounded parts of a high-voltage power circuit breaker. Indeed, conductive particles move towards the highest dielectrically stressed live parts. These particles can lift-off, float or stand-up under the influence of the voltage, reducing the required dielectric clearance and increasing the voltage gradients. This can lead to a dielectric breakdown of the gap between the interrupter and the tank.
In order to assure effective circuit breaker operation, nowadays tanks are equipped with means for trapping the particles.
Particle traps are stationary elements. Their shape is designed to promote the movement of particles so that these are transported under a shielded area in which the electric field intensity is negligible. In this protected region, particle motion due to the electric field is no longer possible.
These particle traps are disposed along the surface of the tank and are generally depressions or cavities formed into the wall of the tank, in which zero or near zero electric fields are created. In operation, particles are guided to the particle trap by an electric field which exists between the live and grounded parts of the circuit breaker and are trapped by the low electric field in the trap.
An example of a particle trap of the prior art (U.S. Pat. No. 6,307,172) is illustrated in FIG. 1 and FIG. 2. It represents a tank 30 with a particle trap 29 in the form of an elongated, recessed channel located on the bottom of the tank, the channel being axially directed relative to a longitudinal axis of the tank and extending substantially between both ends of the tank (FIG. 1 and FIG. 2).
Another example of a particle trap of the prior art (U.S. Pat. No. 7,858,877) is illustrated in FIG. 3. There is a circuit breaker tank 30 with a circular well-shaped particle trap 19. In the illustrated embodiment of the prior art, the bottom wall of the tank is inclined in the direction of the particle traps 19 and the particle traps 19 are covered by covering shrouds 13 having a shielding surface for dielectric shielding of shielding area.
These prior art solutions have the disadvantage that, if a particle stops moving or gets stuck, lodged or obstructed by features on or around the trap where it still can cause a breakdown of the insulation, there is no means to dislodge the particle.